If you itemized your deductions on the 2018 tax return, the entire amount of your CA refund will be considered income in 2019.
If you used the standard deduction on your 2018 tax return, none of your CA refund will be considered income in 2019.
If you need help determining if you used the standard deduction or if you itemized your deductions (you would only have done one), let me know in a comment below.